i think i did the compression test correctly, anyways, on both rotors, i get approximately 80psi bounces, it just bounces to 80psi, too fast for me to say, so i jsut keep on cranking it, and it jsut bounces to 80psi ea time.

then, for a max, i get around 80psi also?..does this sound right?, shouldnt i get a higher pressure for the total compression of alll three cycles??

thanks, ut

 

Mr. UT,

Are you using the mazda rotary specific compression tester? If not I saw a post several weeks back saying their's a "fudge" factor with piston compression testors. Try doing a search to find it.

-- vaughnc

 

no im not, im using a standard compression tester

 

As long as you get three even bounces for each rotor you're fine.&nbsp I bet you didn't even do the compression test as per Mazda spec, which would account for the lower readings.&nbsp To get the numbers Mazda specs, you need to pull BOTH leading plugs out during the entire test.&nbsp Also, you need to prop the throttle to WOT during the test.&nbsp Most people don't even bother to do this, and I'd bet you'd get the 20psi or so that you're missing.

You need to tell us what model you're doing this on, as compression ratios and mileage plays a big part on the absolute numbers...



-Ted

 

Is there ar chart to refer to somewhere? I just got a comp tester for the club, and will soon be expected to know this stuff off the top of my head...

Thanks,

 

80psi???

i got 115's on front and 120's on rear bounicng no lower than 100

just my worthelses 3 cents

 

Nah, it's all about experience...
My rule of thumb is that compression usually starts to fall off at 100,000 miles for a turbo and 150,000 miles for an NA.&nbsp You'll need to also compensate for the different CR's of the different rotor types for all the different Zenki/Kouki and turbo versus NA.

Zenki NA - 9.4:1
Zenki turbo - 8.5:1
Kouki NA - 9.7:1
Kouki turbo - 9.0:1

You could have up to 15psi-20psi of deviation going from the lowest CR (Zenki turbo) to highest CR (Kouki NA).&nbsp For the most part, a Zenki turbo pumping out 100psi is a good motor in my book.&nbsp Kouki NA's can easily pump out 120psi numbers when in good condition.



-Ted

 

Thanks Ted.

 

hmm..pull out tha leading as well?..nope, didnt do tat, thanks for the tip. i will try to give it another try tommorw and let you guys know wat i come up with..
oh, 88 gxl, 140,000+ miles

thanks, ut

 

If you follow the factory compression method.....

YOU do NOT PULL THE LEADING PLUGS.....

Much less pull them at the same time as taking the reading from the TRAILING...

geesh

youll get ZERO compression readings...
think about it.

I agree about the throttle being wide open though, but its not a "requirement".

the max for a 88 series 2nd gen engine is: 85.2 (@9.4:1 ratio)

the max for a 91 series 2nd gen engine is (approx): 89 (9.7:1 ratio)

Both can sustain a 20.1 lb difference in compression MAX.


Remove both trailing plugs, test the rotors with the schrader valve removed.

and no, the compression withthe valve in is not CUMULATIVE (it does not add each time)

it olny holds the MAX pressure you saw on any rotor face.

 

You're right - I'm glad you know how to read the Mazda factory service manual...


We pull both leadings (and plug the compression tester into one of the two leading holes), cause the leading holes that open up into the combustion chamber is larger than the trailings.&nbsp We are not using the Mazda factory digital compression tester that costs $100,000; we base all our compression numbers on our consistent procedures and experience.&nbsp And, no, if you pull both the leading and keep the trailings in, you will NOT get ZERO compression readings...

"think about it"

The leadings give slightly higher compression numbers.



-Ted

 

I didnt say...


I said..

You have to leave ONE plug in....

And the digital Mazda tester runs $1600 at mazdatrix, and goes for a few hundred on ebay each time one shows up.

I keep bidding too low to get one for myself though!

 

Sniper, reread what Ted is saying. He's saying pull both leading plugs, and screw the compression tester into the leading plug hole of the rotor you want to check compression for. Then open the throttle to WOT and do the test (I'm sure with the appropriate fuses removed to avoid spark and fuel)

He's not saying pull the leading, then screw in the tester into the trailing.

PaulC

 

mr ut had midunderstood i think....

if he pulled the trailing AND leading as well, then well, that didnt make sense...

I was referring to his statement about pullign the leadings "as well" as the trailings.....

that was just odd.